Triple sunset system

A newly discovered planet has bountiful sunshine, with not one, not two, but three suns glowing in its sky.

It is the first extrasolar planet found in a system with three stars. How a planet was born amidst these competing gravitational forces will be a challenge for planet formation theories.

"The environment in which this planet exists is quite spectacular," said Maciej Konacki from the California Institute of Technology. "With three suns, the sky view must be out of this world -- literally and figuratively."

The triple-star system, HD 188753, is located 149 light-years away in the constellation Cygnus. The primary star is like our Sun, weighing 1.06 solar masses. The other two stars form a tightly bound pair, which is separated from the primary by approximately the Sun-Saturn distance.

"The pair more or less acts as one star," Konacki told SPACE.com.

The combined mass of the close pair is 1.63 solar masses.

Using the 10-meter Keck I telescope in Hawaii, Konacki noticed evidence for a planet orbiting the primary star. This newfound gas giant is slightly larger than Jupiter and whirls around its central star in a 3.5-day orbit. A planet so close to its star would be very hot.

Although other so-called hot Jupiters have been found in such close-in orbits, the nearby stellar pair in HD 188753 likely sheared off much of the planet making material in the disk that would likely have existed around the primary star in its youth. Since this proto-planetary disk holds the construction materials for planets, there does not appear to be any safe place for this far-off world to have been assembled.

Snow line and migration

The heat coming from a nearby star frustrates the initial stages of giant planet formation -- the gluing together of planetary seeds, called cores. Therefore, the typical hot Jupiter is thought to form farther out -- beyond a theoretical limit called the snow line.

"Past about 3 AU, it is cold enough to form ices and other solid material for building cores," Konacki said. An AU is the distance between the Sun and the Earth -- about 93 million miles.

Once a sufficiently large core is built outside the snow line, the planet can start accreting gas and -- if the conditions are right -- migrate toward its sun.

Although this scenario appears to work in most stellar systems, it has difficulty explaining the newly-discovered planet in HD 188753. Of all the planet-harboring stars known, this is the closest that a stellar companion has ever been found.

"The problem is that the pair is a massive perturber to the system," Konacki said. "Together, these two stars are more massive than the main star."

Moreover, the pair goes around the primary along an oblong orbit that stretches from 6 AU out to 18 AU over a 26 year period. This eccentricity increases the instability of the disk around the primary. Konacki estimates that due to the gravitational perturbations from the pair, the proto-planetary disk was truncated down to 1.3 AU, far within the snow line.

"How that planet formed in such a complicated setting is very puzzling. I believe there is yet much to be learned about how giant planets are formed," Konacki said.

Targeting multiple stars

Konacki hopes to find more planets around stars with companions. About 30 extrasolar planets have been found around double-star systems, or binaries. This is a small percentage of the total number of extrasolar planets, even though multi-star systems outnumber single star systems.

The reason for this disparity is that the main technique for locating planets -- the radial velocity method -- is not well-suited for finding planets with more than one star.

"Single stars are much easier to work with, since the shape of the spectrum stays the same," Konacki explained.

By watching for wobbles in a star's spectrum, astronomers can infer the gravitational tug from a nearby planet. But when there is a companion star, its light competes with that of the main star. Konacki has developed a method to extract the planet wobbles from this messy, combined spectrum.

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If I remember right, dantuween (sp) only had 2, so how well does a solar panel work there?

If I remember right, dantuween (sp) only had 2, so how well does a solar panel work there?

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But the binary pair of suns is orbiting the main star at a distance from about our Sun to Saturn. So the night sky won't be like Dantooine - you'll have a regular sunrise every day, but then the binary pair will be visible irregularly. And it wouldn't surprise me if the binary pair have some moons as well, especially with the mass of 1.63 suns. That is one messed up solar system....

But the binary pair of suns is orbiting the main star at a distance from about our Sun to Saturn. So the night sky won't be like Dantooine - you'll have a regular sunrise every day, but then the binary pair will be visible irregularly. And it wouldn't surprise me if the binary pair have some moons as well, especially with the mass of 1.63 suns. That is one messed up solar system....

D

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So you're saying that there could be planets orbiting the binaries, that are orbiting the primary. Or is the primary orbiting the binaries?

If both the primary and the binaries have orbiting planets, then couldn't those planets conceivably either collide, or shift orbit points (i.e., have something of a Figure-8 orbit)?

It's interesting because I learned the snow line term as frost line in astronomy last year.

Go figure.

Another thing is that this planet is a gas giant, so I don't think you would be able to see the sunset from the planet. Of course I'm sure the planet would have some moons (though who is to say that? there are enough things that aren't "right" about this solar system as it is).

It's interesting because I learned the snow line term as frost line in astronomy last year.

Go figure.

Another thing is that this planet is a gas giant, so I don't think you would be able to see the sunset from the planet. Of course I'm sure the planet would have some moons (though who is to say that? there are enough things that aren't "right" about this solar system as it is).

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Guess that I will just have to keep my residence here on good ol' Earth.

This just goes to show that the universe is a wild place, filled with things that we can not even imagine here on earth.
I do a little backyard astronomy with my little 6" dobson and I am always filled with awe when I see something new to me out in the cosmos. I just wish that as a world community, we were alittle farther on the arc of space exploration. But that isn't going to happen until we get our act together on the planet we already inhabit.

This just goes to show that the universe is a wild place, filled with things that we can not even imagine here on earth.
I do a little backyard astronomy with my little 6" dobson and I am always filled with awe when I see something new to me out in the cosmos. I just wish that as a world community, we were alittle farther on the arc of space exploration. But that isn't going to happen until we get our act together on the planet we already inhabit.

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True, we could stand to get our act together a little bit better than we are currently doing (especially before going to new planets and visiting & colonizing them).

That's not the same one - the one in the article is talking about a main star and a binary orbiting at a distance similar to Saturn.

If you were on a moon of the gas giant, the main sun would overpower the other two - which would just be very, very bright stars. Remember what the sun looks like from Saturn in those pics from Voyager and Cassini?

And if you were at an Earth distance, the binary stars would be brighter, but still not the same as the sun. You might get enough light to see by at night from the binary pair, but I can't imagine it would be more than the light of our own full moon.

[edit] There seems to be some confusion - the CNN article mentions that the planet is at a distance of Saturn and the binary pair is orbiting the primary. I don't know who's right.... [/edit]

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